The correspondents who arrived at the British army’s General Headquarters at St Omer in June 1915 were: William Beach Thomas for the Daily Mail and Daily Mirror; Basil Clarke (1879-1947) for the Amalgamated Press; Philip Gibbs for the Daily Telegraph and Daily Chronicle; Percival Phillips (1877-1937) for the Daily Express; H. Perry Robinson (1859-1930) for The Times and Daily News; and Herbert Russell (1869-1944) of the Reuters news agency. All billeted together in a house in the village of Tatinghem adjacent to St Omer, they were supplied with army servants, army vehicles and dedicated conducting officers. Censors accompanied them at all times. Crucially, they received officer’s uniforms bearing green armbands – normally the insignia of the intelligence services - and the honorary rank of captain.

A google image search on some of those names might turn up a photo in uniform.